1. Field of the Invention
The present invention describes the construction of recombinant Bordetella pertussis strains derived from a parent strain designated Tohama and using vector pSS4245 for integration of mutations and additional copies of genes.
2. Description of Related Art
Pertussis or whooping cough is a severe infant disease caused by Bordetella pertussis infection of the upper respiratory tract [1]. Vaccines have been available for decades, which consist of killed whole cells of B. pertussis. They are administered as trivalent Diphtheria-Tetanus-Pertussis combination or newer combinations providing also immunity against Hepatitis B and Haemophilus influenzae type b invasive disease [2]. The use of whole-cell vaccines has been reduced, discouraged or even banned in a few countries due to their questionable safety profile, which is due to high levels of endotoxin and other bacterial toxins associated with the killed whole cells [3, 4].
Acellular vaccines, named after the fact that they do not contain whole cells but only partially or extensively purified bacterial antigens, were introduced in Japan in 1981 [5]. The higher purity of the component antigens in acellular vaccines translated to an improved clinical safety profile. These vaccines were introduced in the mid-90s in industrialized countries after extensive field trials which demonstrated their safety and efficacy [6]. A broader introduction by WHO into the Expanded Program of Immunization was, however, hampered by the significantly higher cost of acellular vaccines.
A major virulence factor of B. pertussis is Pertussis Toxin (PT) [7, 8] and pertussis toxoid (PTd) is the principal antigen in acellular vaccines [8]. Unlike Diphtheria and Tetanus toxins, which can be inactivated by simple treatment with formaldehyde, PT proved more difficult to inactivate by chemical means [9]. Currently different inactivation processes are in use for commercial production. All have in common extensive denaturation of PT caused by the chemical treatment. Two candidate vaccines were explored using a genetically inactivated toxin (rPT) [10-12] and one of these candidates was included in a field efficacy trial [11-12].
Vaccines containing rPT are, however, not yet available.